Astrid R. Taylor

Functional identity and diversity of animals predict ecosystem functioning better than species-based indices

Drastic biodiversity declines have raised concerns about the deterioration of ecosystem functions and have motivated much recent research on the relationship between species diversity and ecosystem functioning. A functional trait framework has been proposed to improve the mechanistic understanding of this relationship, but this has rarely been tested for organisms other than plants. We analysed eight datasets, including five animal groups, to examine how well a trait-based approach, compared with a more traditional taxonomic approach, predicts seven ecosystem functions below- and above-ground. Trait-based indices consistently provided greater explanatory power than species richness or abundance. The frequency distributions of single or multiple traits in the community were the best predictors of ecosystem functioning. This implies that the ecosystem functions we investigated were underpinned by the combination of trait identities (i.e. single-trait indices) and trait complementarity (i.e. multi-trait indices) in the communities. Our study provides new insights into the general mechanisms that link biodiversity to ecosystem functioning in natural animal communities and suggests that the observed responses were due to the identity and dominance patterns of the trait composition rather than the number or abundance of species per se.

PLFA profiles of microbial communities in decomposing conifer litters subject to moisture stress

Abstract The influence of moisture stress on microbial communities in decomposing coniferous litters was investigated using phospholipid fatty acid (PLFA) profiling. Studies were carried out in German and Greek forest plots under contrasting climatic conditions from the late summer to the early winter periods. Litterbags containing spruce (Germany) or pine (Greece) needles were subjected to different irrigation treatments over 4 months. The influences of climate and litter type on microbial community structure were larger than those imposed by irrigation or moisture stress treatments. In the German spruce litter, the PLFA signatures indicated that there was initially a larger bacterial than fungal biomass and both components decreased with time. Concentrations of individual PLFA, proportions of PLFA subgroups and principal component (PC) scores showed that, apart from sample date, mesh size was more important than irrigation treatment in determining microbial community structure; though treatment effects were less apparent in the third (winter) sample. Pine litter in the Greek site, with a Mediterranean climate, had a larger fungal than bacterial biomass. Little effect of treatment on individual PLFA concentrations or PC scores was measured, though both fungal and bacterial communities increased significantly with regular irrigation in the third (winter) sample. Effects of mesh size in the German spruce litter were related to differences in the abundance of microarthropods. This effect was absent from the Greek pine litter where there was a relatively low abundance of fauna. The final spruce litter sample, taken in winter, exhibited very different PC scores from other samples, suggesting marked changes in the microbial community in response to snow melt. Certain long chain fatty acids associated with eukaryotes were only found on this occasion. This study has shown that structure of bacterial communities associated with decomposing conifer litters is highly sensitive to changes in environmental conditions. There was, however, little indication that these differences in biota were functionally important for the initial phases of plant litter decomposition.

Relative importance of local- and large-scale drivers of alpine soil microarthropod communities

Nitrogen (N) deposition and climate are acknowledged drivers of change in biodiversity and ecosystem function at large scales. However, at a local scale, their impact on functions and community structure of organisms is filtered by drivers like habitat quality and food quality/availability. This study assesses the relative impact of large-scale factors, N deposition and climate (rainfall and temperature), versus local-scale factors of habitat quality and food quality/availability on soil fauna communities at 15 alpine moss–sedge heaths along an N deposition gradient in the UK. Habitat quality and food quality/availability were the primary drivers of microarthropod communities. No direct impacts of N deposition on the microarthropod community were observed, but induced changes in habitat quality (decline in moss cover and depth) and food quality (decreased vegetation C:N) associated with increased N deposition strongly suggest an indirect impact of N. Habitat quality and climate explained variation in the composition of the Oribatida, Mesostigmata, and Collembola communities, while only habitat quality significantly impacted the Prostigmata. Food quality and prey availability were important in explaining the composition of the oribatid and mesostigmatid mite communities, respectively. This study shows that, in alpine habitats, soil microarthropod community structure responds most strongly to local-scale variation in habitat quality and food availability rather than large-scale variation in climate and pollution. However, given the strong links between N deposition and the key habitat quality parameters, we conclude that N deposition indirectly drives changes in the soil microarthropod community, suggesting a mechanism by which large-scale drivers indirectly impacts these functionally important groups.

Diversity and Role of the Decomposer Food Web

Only a small part of primary production is consumed by phytophagous organisms (Ellenberg et al. 1986). It is generally agreed that the food web based on detritus is more important for the flow of energy and nutrients through terrestrial ecosystems than the food web based directly on autotrophic production (Swift et al. 1979). The decomposer community that is responsible for this flow is composed of microorganisms and invertebrates. The major components of the decomposer microorganisms are bacteria and fungi. The dominant decomposer fauna groups belong to the Protozoa, Nematoda, Oligochaeta and Arthropoda Fig. 17. There is evidence that the effects of soil organisms on ecosystem functioning critically depend on both the structural diversity of the decomposer community and environmental conditions (Freckman 1994; Hall 1996). However, little information is available concerning the impact of soil biodiversity on the integrity, function and sustain ability of terrestrial ecosystems (Wolters 1998a).